About your first question: the important point is that you need to have a modeling procedure that assures the pipeline end shall receive a displacement corresponding to the length VAL-to-end. I understand that your results confirm that, with a VAL estimated as 250 m, truncating the model to 250m does not assure this goal. How to solve this problem is after you. Of course placing an anchor beyond VAL, even makes sense, is not only ugly but also shall rise a lot of question marks from others. In the end, just keep in mind that the soil cannot be modeled exactly and software cannot simulate the continuous contact pipeline-soil, so small differences in results are not significant.

About the second point, I'll try to make a compilation from Mr. Diehl's article.

If you are running large radius (50*OD) bends (or any other radius for that matter) through the buried pipe modeler, you can add a node at the start and end of each bend. "Bury" only the bends (by specifying a soil model number for these segments) by click on "bury the system".
Once the program listed "Model conversion complete", instead of clicking on either the "OK" or "Cancel" buttons at the bottom of the window, click on the Close (X) button at the top right corner of the window. After this first step, the restraints shall be not added and control shall be returned to the Underground Pipe Generator and yo can find that the model now has extra soil model nodes. The effect is that node density is automatically increased for bends. The modeler shall maintain the bend designation through these back-to-back "partial" bends so each extra node is a change in direction with a bend.
All you need to do is to continue in the buried pipe modeler and bury this modified model once again, this time bury all sections that should be buried.

The short version is exactly what Mr. Diehl said "That undocumented "feature" is to "rebury" the buried section where extra nodes are desired."

I would add that in the last time I haven't used this procedure so I cannot say how is functioning in the last versions.